1. Field of the Invention
This invention relates to improvements in the operation of a sheet decurler in a photocopying machine. More particularly, this invention has a decurler apparatus which automatically adjusts the tension in the decurler for adjusting the amount of decurling in a copy sheet.
2. Description of the Related Art
In an electrophotographic application such as xerography, a charge retentive surface is electrostatically charged. A light pattern formed from the original image to be reproduced selectively discharges the charge of a retentive surface. The resulting pattern, a combination of charge and discharge areas on the charge retentive surface, form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". The toner is held on the image area by electrostatically charging the surface. Thus, a toner image is produced in conformity with a light image of the original beam produced. The toner image may then be transferred to a substrate (e.g., paper), and the toner is fused onto the substrate by passing through a fuser. The substrate with the affixed latent image has some degree of curl to it. The substrate is forwarded through a decurling apparatus to remove the curl of the substrate. Then the substrate is either ejected from the machine to a holding tray or is re-routed through the machine for a second side copy.
The electrophotographic process is well known, and is useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be discharged in a variety of ways. Ion projection devices where charge is imagewise deposited on a charge retentive surface operate similarly.
The curl of the substrate could affect the proper stacking or correlating of the copy machine output. The curl occurs during the fusing process. In the fuser, heat is applied to the image side of the copy sheet to fuse the toner to the substrate. When the heat is applied, the moisture dries on the one side of the copy sheet. The difference in the moisture level between the fused side and the other side of the copy sheet produces substantial differences in curl. The high moisture content in the copy paper may be due to storage of the paper in a high ambient humidity level or in the copy machine. Differences in the amount of curl will also occur in accordance with the weight of a copy paper.
Prior decurling devices feed individual cut sheets through the decurling mechanisms which are adjustable to compensate for varying sheet curls depending upon ambient conditions and sheet characteristics. This mechanism must be manually adjusted each time a different type of copy sheet is used. It is difficult to obtain the exact amount of straightening necessary due to the variable curling, from day to day and from the use of various papers in a wide range of paper weight and different curl characteristics.
A typical belt and roller decurler apparatus use a roller to penetrate into a belt to have paper conform to a given radius.